Preparation of 1-O-Acyl-D-GlycopyranosesviaChloroacetylated Glycopyranosyl Donors

Abstract

Various 2,3,4,6-tetra-O-chloroacetyl-D-glucopyranosyl donors 2 were coupled to cinnamic acid (3a) and silver cinnamate (4a) to give the corresponding chloroacetylated 1-O-cinnamoyl-glucopyranose 5a in good yields. The highest α-selectivity (α/β = 87:13) was achieved by coupling of the α-fluoride 2c with 3a under boron trifluoride catalysis whereas the α-bromide 2g afforded exclusively β-5a upon treatment with 4a. Thus, the D-glucosyl donors 2c and 2g and 2, 3, 4, 6-tetra-O-chloroacetyl-α-D-galactopyranosyl bromide (6) were condensed with a series of acids 3a-e (cinnamic, 2-methyl-4-pentenoic, 3, 4, 5-trimethoxybenzoic, oleic, and 4-chloroacetoxy cinnamic acid, respectively) and silver salts 4a-d thereof. From α/β-mixtures 5a-c and 5e obtained from 2c and the respective acid 3, the α-products were isolated in moderate yield. Selected examples of thus prepared 1-O-acyl-D-glucoses 5 and D-galactoses 7 were dechloroacetylated using 1-piperidinethiocarbamide to give the corresponding unblocked 1-O-acyl monosaccharides 8 and 9 in 52-64% yield.